The present invention relates to a sheet discharging device that sequentially places sheets on which images are formed using an image forming apparatus such as a printer, copier, or a printing machine, at a predetermined position on a tray, and a sheet postprocess apparatus that executes a postprocess such as stapling, punching, or stamping on the sheets placed on the tray.
To automate a series of processes including copying and printing, postprocess apparatuses are commonly used which temporarily place sheets on which images are formed using an image forming apparatus, on a tray and which then execute a postprocess such as stapling, punching, or stamping on the sheets. The sheets (or a bundle of sheets) postprocessed on the temporary tray are then accommodated in a downstream accumulating tray. When the sheets are thus conveyed to the tray, the correct postprocess can be achieved only if the sheets are orderly transferred to a predetermined position. However, with increases in the speed of the image forming apparatus and in the number of colors used in the apparatus, sheets are more likely to be curled at high temperature. Further, sheets the surfaces of which are coated exert only a small frictional force and are thus difficult to convey. This requires a conveying mechanism that conveys sheets from a sheet discharging port to a predetermined position on the tray.
For example, a conveying belt disclosed in Japanese Patent Laid-Open No. 2002-241015 is known as a mechanism that conveys sheets from the sheet discharging port to the tray. This document describes an endless belt (hereinafter referred to as a caterpillar belt) supported by a pair of pulleys and placed between the sheet discharging port and the tray so that the tray-side pulley can pivot around the sheet discharging port-side pulley in a vertical direction. Accordingly, a sheet from the sheet discharging port is conveyed on a top surface of the belt to the tray. The sheet is then conveyed in the reverse conveying direction by a bottom surface of the belt to abut against a regulating member. When the sheet is switched back on the caterpillar belt and transferred to the predetermined position on the tray, the sheet is reliably conveyed into the tray to prevent incomplete discharging resulting from the trailing end of the sheet remaining at the sheet discharging port. This mechanism is also characterized in that the conveyed sheet can be conveyed to the predetermined position on the tray by the bottom surface of the belt.
When the caterpillar belt is pivotably hung between the sheet discharging port and the tray and moved in the vertical direction depending on the number of sheets loaded on the tray, the following problems may occur. To convey a sheet on the top surface of the belt from the sheet discharging port to the tray, a conveyance guide is required which guides the sheet while sandwiching it between components of the guide. The conveyance guide and the belt conventionally press the sheet by their own weights. Thus, to be conveyed into the tray, the sheet is sandwiched between the conveyance guide and the belt and guided to the tray. After being conveyed into the tray, the sheet is sandwiched between the bottom surface of the belt or the uppermost sheet accumulated on the tray and transferred to the predetermined position. For design conditions for the conveyance guide and belt, it is difficult to set stable conveyance conditions for a wide variety of sheets such as thin paper, which is likely to be curled, and glossy paper, the surface of which is coated.
If the conveyance guide is reduced to allow a sheet to advance more easily between the conveyance guide and the belt top surface, then with thick glossy paper like colored paper, the sheet trailing end may remain on the belt to prevent the sheet from being appropriately discharged. With thin sheets, which are likely to be curled, when a sheet conveyed onto the tray is reversed and guided to the belt bottom surface, the curled sheet trailing end may advance between the belt top surface and the conveyance guide to cause jamming. An increase in the pressing force of the conveyance guide may prevent the curled thin sheet from advancing from the sheet discharging port to the belt top surface, thus causing jamming. Similarly, an increase in the contact force between the belt bottom surface and the tray may exert a stronger conveying force on accumulated sheets to damage them, for example, wrinkle them. In contrast, a decrease in contact force may disadvantageously preclude a sheet advanced onto the tray from being reliably transferred to the predetermined position.
The present invention has been made in view of the above problems. A main object of the present invention is to provide a sheet discharging device with a simple structure which can reliably convey a wide variety of sheets onto a tray by adjusting the magnitudes of the pressing forces of a conveyance guide and a caterpillar belt according to the position of the sheet transferred from a sheet discharging port to a predetermined position on the tray, the sheet discharging device being able to then reliably transfer the conveyed sheet to a predetermined position on the tray, as well as a sheet postprocess apparatus using the sheet discharging device.
The other objects and features of the present invention will be clarified in the description below of an embodiment based on the accompanying drawings.